Human or animal body fluids can be measured in-vivo to determine analyte concentrations, such as glucose. The measurement system comprises an exchangeable sensor for in-vivo placement, a data carrier with calibration data for the sensor, a housing having a first chamber for receiving a sterile sensor and a second chamber for receiving a data carrier, and a base station that couples to the housing for transmitting measurement signals to an evaluation unit. Replacement sterile sensors can be packaged in a sterile package and the data carrier associated with the replacement sensor can be packaged in a non-sterile package.